[159.02] A Strong Test of Nova Trigger Theory

B. E. Schaefer (Louisiana S. U.)

Theoretical models of novae are robust, however the aspect
of what triggers the eruption has not been tested
observationally. From theory, for a particular white dwarf,
the nova should be triggered when a certain amount of matter
has accreted, which implies that the inter-eruption time
interval (T) should vary inversely with the average
accretion rate which should scale as the average B-band
intensity, I (or perhaps as a low power of I to account for
unknown bolometric corrections). This strong prediction can
be tested only on recurrent novae with a complete record
with three or more eruptions and without a red giant
companion (i.e., only T Pyx and U Sco). I have collected
large numbers of B-band magnitudes from the Harvard plate
stacks, the UK Schmidt, and the literature over many nights.

For T Pyx, the eruptions were at 1890.4, 1902.3, 1920.3,
1944.9, and 1967.0. The four inter-eruption intervals (with
T equal to 11.9, 18.0, 24.6, and 22.1 years) have 13, 7, 68,
and 29 nights of observation resulting in average magnitudes
of 14.32, 14.74, 14.88, and 14.72 mags (I equal to ==1,
0.73, 0.66, and 0.75) respectively. The products are 11.9,
13.1, 16.2, and 16.6 for T*I and 11.9, 9.6, 10.7, and 12.4
for T*I2.

For U Sco, the last four eruptions were at 1969.1, 1979.5,
1987.4, and 1999.2. The three inter-eruption intervals (with
T equal to 10.4, 7.9, and 11.8 years) have 2, 4, and 26
nights of observation resulting in average magnitudes of
18.44, 18.30, and 18.52 mags (I equal to ==1, 1.14, and
0.94) respectively. The products are 10.4, 9.0, and 11.1 for
T*I and 10.4, 10.3, and 10.4 for T*I2.

We see that the novae are relatively bright during short
inter-eruption intervals and dim during long intervals. The
simple (i.e., no bolometric correction) product T*I is
constant to 16% for T Pyx and 11% for U Sco. The RMS
scatter in the product is minimized for intensities raised
to powers of ~ 2 (i.e., T*I2), with 11% scatter for
T Pyx and 0.6% scatter for U Sco. I regard this as a
confident and critical confirmation of the theory of nova
triggers.

Since their last eruptions, T Pyx is nearly constant at
15.49 mag (92 nights, I=0.37) while U Sco is close to 18.47
mag (14 nights, I=1.00). I predict T Pyx will go off next in
2019-2057 and that U Sco will next go off in 2009.5±1.0.

The author(s) of this abstract have provided an email address
for comments about the abstract:
schaefer@lsu.edu